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Gol’tsman, G. N., & Gershenzon, E. M. (1993). High speed hot-electron superconducting bolometer. In J. R. Birch, & T. J. Parker (Eds.), Proc. SPIE (Vol. 2104, pp. 181–182). SPIE.
Abstract: Physical limitation of response time of a superconducting bolometer as well as the nature of non-equilibrium detection of radiation have been investigated for Al, Nb and NbN thin films in spectral range from submillimeter to near-infraredwavelengths [1,2]. In the case of ideal heat removal from the film with the f_‘. 100A thickness the detection mechanism is an electron heating effect that is not selective to radiation wavelength in a very broad range. The response time ofan electron heating bolometer is determined by an electron-phonon interaction time. This time is of about 10 ns, 0.5 ns and 20 ps for Al, Nb, and NbN correspondingly near the critical temperature of the superconducting film. Thesensitive area of the bolometer consists of a number of narrow strips (with awidth of 1µm) connected in parallel to contact pads; these pads together witha sapphire substrate and a ground plate represent the microstrip transmissionline with an impedance of 50 Q.
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Cherednichenko, S., Ronnung, F., Gol'tsman, G., Gershenzon, E., & Winkler, D. (1999). YBa2Cu3O7-δ hot-electron bolometer with submicron dimensions. In Proc. 10th Int. Symp. Space Terahertz Technol. (pp. 181–189).
Abstract: Photoresponse of YBa2Cu3O7-δ hot-electron bolometers to modulated near-infrared radiation was studied at a modulation .frequenc y var y ing from 0.2 MHz to 2 GHz. Bolometers were _fabricated from a 50 12 M thick film and had in-plane areas of 10x10 , um 2 . 2x0.2 s um', 1x0.2 p.m', and 0.5x0.2 jim. We found that nonequilibrium phonons cool down more effectively for the bolometers with smaller area. For the smallest bolometer the bolometric component in the response is 10 dB less than for the largest one.
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Hübers, H. - W., Schubert, J., Krabbe, A., Birk, M., Wagner, G., Semenov, A., et al. (2001). Parylene anti-reflection coating of a quasi-optical hot-electron-bolometric mixer at terahertz frequencies. Infrared Physics & Technology, 42(1), 41–47.
Abstract: Parylene C was investigated as anti-reflection coating for silicon at terahertz frequencies. Measurements with a Fourier-transform spectrometer show that the transmittance of pure silicon can be improved by about 30% when applying a layer of Parylene C with a quarter wavelength optical thickness. The 10% bandwidth of this coating extends from 1.5 to 3 THz for a center frequency of 2.3–2.5 THz, where the transmittance is constant. Heterodyne measurements demonstrate that the noise temperature of a hot-electron-bolometric mixer can be reduced significantly by coating the silicon lens of the hybrid antenna with a quarter wavelength Parylene C layer. Compared to the same mixer with an uncoated lens the improvement is about 30% at a frequency of 2.5 THz.
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Karasik, B. S., Lindgren, M., Zorin, M. A., Danerud, M., Winkler, D., Trifonov, V. V., et al. (1994). Picosecond detection and broadband mixing of near-infrared radiation by YBaCuO films. In M. Nahum, & J. - C. Villegier (Eds.), Proc. SPIE (Vol. 2159, pp. 68–76). Spie.
Abstract: Nonequilibrium picosecond and bolometric responses of YBCO films 500 angstroms thick patterned into 20 X 20 micrometers 2 size structure to 17 ps laser pulses and modulated radiation of GaAs and CO2 lasers have been studied. The modulation frequencies up to 10 GHz for GaAs laser and up to 1 GHz for CO2 were attained. The use of small radiation power (1 – 10 mW/cm2 for cw radiation and 10 – 100 nJ/cm2 for pulse radiation) in combination with high sensitive read-out system made possible to avoid any non-linear transient processes caused by an overheating of sample above a critical temperature or S-N switching enhanced by an intense radiation. Responses due to the change of kinetic inductance were believed to be negligible. The only signals observed were caused by a small change of the film resistance either in the resistive state created by a bias current or in the normal state. The data obtained by means of pulse and modulation techniques are in agreement. The responsivity about 1 V/W was measured at 1 GHz modulation frequency both for 0.85 micrometers and 10.6 micrometers wavelengths. The sensitivity of high-Tc fast wideband infrared detector is discussed.
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Gerecht, E., Musante, C. F., Zhuang, Y., Yngvesson, K. S., Gol’tsman, G. N., Voronov, B. M., et al. (1999). NbN hot electron bolometric mixerss—a new technology for low-noise THz receivers. IEEE Trans. Appl. Supercond., 47(12), 2519–2527.
Abstract: New advances in hot electron bolometer (HEB) mixers have recently resulted in record-low receiver noise temperatures at terahertz frequencies. We have developed quasi-optically coupled NbN HEB mixers and measured noise temperatures up to 2.24 THz, as described in this paper. We project the anticipated future performance of such receivers to have even lower noise temperature and local-oscillator power requirement as well as wider gain and noise bandwidths. We introduce a proposal for integrated focal plane arrays of HEB mixers that will further increase the detection speed of terahertz systems.
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0kunev, 0., Dzardanov, A., Ekstrom, H., Jacobsson, S., Kollberg, E., Gol'tsman, G., et al. (1994). NbN hot electron waveguide mixer for 100 GHz operation. In Proc. 5th Int. Symp. Space Terahertz Technol. (pp. 214–224).
Abstract: NbN is a promising superconducting material used to develope hot- electron superconducting mixers with an IF bandwidth over 1 GHz. In the 100 GHz frequency range, the following parameters were obtained for NbN films 50 A thick: the noise temperature of the receiver (DSB) 1000 K; the conversion losses 10 d13, the IF bandwidth 1 GHz; the local oscillator power 1 /LW. An increase of NbN film thickness up to 80-100 A and increase of working temperature up to 7-8 K, and a better mixer matching may allow to broader the IF band up to 3 Gllz, to reduce the conversion losses down to 3-5 dB and the noise tempera- ture down to 200-300 K.
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Gol'tsman, G. N., Karasik, B. S., Okunev, O. V., Dzardanov, A. L., Gershenzon, E. M., Ekstrom, H., et al. (1995). NbN hot electron superconducting mixers for 100 GHz operation. IEEE Trans. Appl. Supercond., 5(2), 3065–3068.
Abstract: NbN is a promising superconducting material for hot-electron superconducting mixers with an IF bandwidth larger than 1 GHz. In the 1OO GHz frequency range, the following parameters were obtained for 50 /spl Aring/ thick NbN films at 4.2 K: receiver noise temperature (DSB) /spl sim/1000 K; conversion loss /spl sim/10 dB; IF bandwidth /spl sim/1 GHz; and local oscillator power /spl sim/1 /spl mu/W. An increase of the critical current of the NbN film, increased working temperature, and a better mixer matching may allow a broader IF bandwidth up to 2 GHz, reduced conversion losses down to 3-5 dB and a receiver noise temperature (DSB) down to 200-300 K.
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Gol'tsman, G., Jacobsson, S., Ekstrom, H., Karasik, B., Kollberg, E., & Gershenzon, E. (1994). Slot-line tapered antenna with NbN hot electron mixer for 300-360 GHz operation. In Proc. 5th Int. Symp. Space Terahertz Technol. (pp. 209–213a).
Abstract: NbN hot-electron mixers combined with slot-line tapered antennas on Si wdnitride membranes had been fabricated. Several strips of 1 gm wide and 5 tan long made from 100 A NbN film are inserted into the slot antenna. IV-curves under local oscillator power in 300-350 GHz frequency range and conversion gain dependencies on intermediate fre- quency in the 0.1-1 GHz range are measured and compared with that for 100 GHz frequency band. Our results show that pumped IV-curves and intermediate frequency bands are different for 100 GHz and 300 GHz frequency ranges. The interpretation exploits the fact that for the lowest radiation frequency the superconducting energy gap is larger than the radiation quantum energy while they are comparable at the higher frequency. Tha results show that such mixers have good perspectives for terahertz receiving technology.
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Gerecht, E., Musante, C. F., Jian, H., Yngvesson, K. S., Dickinson, J., Waldman, J., et al. (1999). New results for NbN phonon-cooled hot electron bolometric mixers above 1 THz. IEEE Trans. Appl. Supercond., 9(2), 4217–4220.
Abstract: NbN Hot Electron Bolometric (HEB) mixers have produced promising results in terms of DSB receiver noise temperature (2800 K at 1.56 THz). The LO source for these mixers is a gas laser pumped by a CO/sub 2/ laser and the device is quasi-optically coupled through an extended hemispherical lens and a self-complementary log-periodic toothed antenna. NbN HEBs do not require submicron dimensions, can be operated comfortably at 4.2 K or higher, and require LO power of about 100-500 nW. IF noise bandwidths of 5 GHz or greater have been demonstrated. The DC bias point is also not affected by thermal radiation at 300 K. Receiver noise temperatures below 1 THz are typically 450-600 K and are expected to gradually approach these levels above 1 THz as well. NbN HEB mixers thus are rapidly approaching the type of performance required of a rugged practical receiver for astronomy and remote sensing in the THz region.
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Lindgren, M., Zorin, M. A., Trifonov, V., Danerud, M., Winkler, D., Karasik, B. S., et al. (1994). Optical mixing in a patterned YBa2Cu3O7-δ thin film. Appl. Phys. Lett., 65(26), 3398–3400.
Abstract: Mixing of 1.56 µm infrared radiation from two lasers in a high quality YBa2Cu3O7-δ thin film, patterned to parallel strips, was demonstrated. A mixer bandwidth of 18 GHz, limited by the measurement system, was obtained. A model based on nonequilibrium electron heating gives a good fit to the data and predicts an intrinsic mixer bandwidth in excess of 100 GHz, operating in the whole infrared spectrum. Reduction of bolometric effects and ways to decrease the conversion loss of the mixer is discussed. The minimum conversion loss is expected to be ~10 dB.
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Gershenzon, E. M., Gol'tsman, G. N., Multanovskii, V. V., & Ptitsyna, N. G. (1979). Capture of photoexcited carriers by shallow impurity centers in germanium. Sov. Phys. JETP, 50(4), 728–734.
Abstract: Measurements were made of the lifetimes rf of free carriers and the relaxation time 7, of the submillimeter impurity photoconductivity when carriers are captured by attracting shallow donors and acceptom in Ge. It is nod that in samples with capture-center concentration N,Z 10"cm-' the relaxation time 7, greatly exceeds rf in the temperature range 4.2-12 K. The measured values of 7,- are compared with the calculation of cascade recombination by the classical model. To evaluate the data on T,, the distinguishing features of this model are considered for the nonstationary case. The substantial difference betweea the values of rf and T, is attributed to re-emission of the carriers from the excited states of the shallow impurities.
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Varyukhin, S. V., Zakharov, A. A., Gershenzon, E. M., Gol'tsman, G. N., Ptitsina, N. G., & Chulkova, G. M. (1990). Low energy excitation in La2CuO4. Sverkhprovodimost': Fizika, Khimiya, Tekhnika, 3(5), 832–837.
Abstract: Measurements of transmission and photoconductivity spectra in submillimeter wave length range as well as of capacity C and conductivity G in the region of acoustic frequencies of metal-dielectric-La2CuO4 system at low temperatures are performed using La2CuO4 monocrystals. Optical spectra posses a threshold character, a sharp decrease of transmission and photocoductivity signal occurs in the energy region hν>1.5 MeV. C(ω,T) and G(ω, T) dependences have a universal form typical of Debye type relaxation processes. Relaxation time dependence is of thermoactivated character τ(T)∼exp(ξ/T) with the gap value ξ≅2 meV. It is assumed that excitations with characteristic energy of ∼2 meV exist in La2CuO4. A possible nature of the detected low-energy excitations is discussed.
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Kawamura, J., Blundell, R., Tong, C. -yu E., Gol’tsman, G., Gershenzon, E., Voronov, B., et al. (1997). Low noise NbN lattice-cooled superconducting hot-electron bolometric mixers at submillimeter wavelengths. Appl. Phys. Lett., 70(12), 1619–1621.
Abstract: Lattice-cooled superconducting hot-electron bolometric mixers are used in a submillimeter-wave waveguide heterodyne receiver. The mixer elements are niobium nitride film with 3.5 nm thickness and ∼10 μm2 area. The local oscillator power for optimal performance is estimated to be 0.5 μW, and the instantaneous bandwidth is 2.2 GHz. At an intermediate frequency centered at 1.4 GHz with 200 MHz bandwidth, the double sideband receiver noise temperature is 410 K at 430 GHz. The receiver has been used to detect molecular line emission in a laboratory gas cell.
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Kawamura, J., Blundell, R., Tong, C. - Y. E., Papa, D. C., Hunter, T. R., Paine, S. N., et al. (2000). Superconductive hot-electron-bolometer mixer receiver for 800-GHz operation. IEEE Trans. Microw. Theory Techn., 48(4), 683–689.
Abstract: In this paper, we describe a superconductive hot-electron-bolometer mixer receiver designed to operate in the partially transmissive 350-μm atmospheric window. The receiver employs an NbN thin-film microbridge as the mixer element, in which the main cooling mechanism of the hot electrons is through electron-phonon interaction. At a local-oscillator frequency of 808 GHz, the measured double-sideband receiver noise temperature is TRX=970 K, across a 1-GHz intermediate-frequency bandwidth centered at 1.8 GHz. We have measured the linearity of the receiver and the amount of local-oscillator power incident on the mixer for optimal operation, which is PLO≈1 μW. This receiver was used in making observations as a facility instrument at the Heinrich Hertz Telescope, Mt. Graham, AZ, during the 1998-1999 winter observing season.
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Yazoubov, P., Kroug, M., Merkel, H., Kollberg, E., Gol'tsman, G., Lipatov, A., et al. (1998). Quasioptical NbN phonon-cooled hot electron bolometric mixers with low optimal local oscillator power. In Proc. 9th Int. Symp. Space Terahertz Technol. (pp. 131–140).
Abstract: In this paper, the noise perform.ance of NIN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixers is investigated in the 0.55-1.1 THz frequency range. The best results of the DSB noise temperature are: 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz and 1250 K at 1.1 THz. The water vapor in the signal path causes a significant contribution to the measured noise temperature around 1.1 THz. The required LO power is typically about 60 nW. The frequency response of the spiral antenna+lens system is measured using a Fourier Transform Spectrometer with the HEB operating in a detector mode.
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